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Stachybotrys chartarum, also known by an old name as Stachybotrys atra, is a cellulose degrading fungus commonly found in soil and on materials rich in cellulose such as hay, straw, cereal grains, plant debris, wood pulp, paper, and cotton. It produces a mass of wet spores sticking together giving the appearance of black pin-heads. The spores (referred to as conidia) are single-celled and ornamented. In indoor environment Stachybotrys thrives on wet cellulose containing material such as drywall and wallpaper. It is thus common in buildings with mechanical or structural defects that result to moisture damage or dampness. It has been isolated from very wet gypsum board/walls and wallpaper; asbestos building substitute; HVAC humidifier water and fans. Although Stachybotrys chartarum mainly survives as a saprophyte (i.e., by feeding on dead organic material), it has also been reported to cause root lesions on soybeans.
Why is Stachybotrys chartarum so feared?
The health effects attributed to Stachybotrys chartarum are controversial. It is generally agreed that Stachybotrys chartarum can potentially cause allergic reactions from inhaled spores and also poses the threat of mycotoxin poisoning. However, there is still debate as to whether this mould is the sole cause of various illnesses as reported in the literature. One of the recent disputed claims is the idiopathic pulmonary hemorrhage that resulted in deaths of infants in Cleveland, Ohio, USA, in 1993-1994. The publicity of this incidence and that of mould related legal cases where Stachybotrys was mentioned has fuelled the public fear for this mould. The situation has been worsened by the news media and some "Mould Experts" by referring to this mould as "deadly toxic mould" and "deadly black mould".
What is known about Stachybotrys chartarum and ill-health?
The first reports associating Stachybotrys chartarum with ill-health dates back to the 1930s. Horses and other animals fed with straw and grains in Ukraine and other parts of eastern Europe developed disease symptoms such as irritation of the mouth, throat, and nose; shock; dermal necrosis; a decrease in leukocytes; hemorrhage; nervous disorder; and death. Russian scientists, in 1938, conducted intensive studies and demonstrated that these symptoms were due to mycotoxins produced by Stachybotrys chartarum that had grown on the cellulose rich straw. The disorders were subsequently named stachybotryotoxicosis. There are reports of stachybotryotoxicosis in farm workers who handled contaminated straw. Recent studies have shown spores of Stachybotrys chartarum to contain high concentrations of highly toxic mycotoxins. As mentioned earlier, in 1993-1994, an outbreak of pulmonary hemorrhage in infants in Cleveland, Ohio,USA, was initially attributed to Stachybotrys chartarum. Although studies associating the outbreak with this mould were later reviewed and the reviewers found little evidence to associate the disease with Stachybotrys chartarum, there are still no studies to date to prove or disapprove this association.
Current knowledge about Stachybotrys chartarum
- Stachybotrys chartarum appears to be a species complex.
Recent studies seem to suggest that Stachybotrys chartarum consist of closely related individuals in which case it is a species complex. What exactly constitutes Stachybotrys chartarum still remains unresolved. Strains of moulds currently referred to as Stachybotrys chartarum are morphologically and biochemically highly variable. Recently what used to be referred to as Stachybotrys chartarum has been separated into one other distinct species and 2 other strains that were only different from each other by secondary metabolites profiles. The distinct species was named Stachybotrys chlorohalonata. Stachybotrys chartarum and Stachybotrys chlorohalonata require an experienced mycologist to differentiate. The uncertainty of what strains constitutes Stachybotrys chartarum may explain in part the current confusion concerning the health effects attributed to this mould.
- Not all Stachybotrys chartarum strains produce mycotoxins
Both toxin and non-toxin producing strains of Stachybotrys chartarum have been isolated from cellulose-based agricultural materials and from contaminated moist building materials. Toxin producers produce a number of potent mycotoxins including trichothecenes Roridin E, Verrucarin J, and Satratoxin H. Trichothecenes are capable of inhibiting the synthesis of DNA, RNA, and protein. These toxins are present on the spore surface, and therefore can be inhaled into the lungs. Studies have also shown that Stachybotrys chartarum trichothecenes can become airborne not only in association with intact spores but also with particles smaller than spores such as fungal fragments. It is, however, not known what level of mycotoxin must be present in the air to affect human health. There is still insufficient evidence supporting a causal relationship between symptoms or illness among building occupants and exposure to mycotoxins.
References
D. -W. Li, C. S. Yang (2005). Taxonomic history and current status of Stachybotrys chartarum and related species. Indoor Air, 15 (9), 5.
B. Andersen, K. F. Nielsen, U. Thrane, M. Cruse, J. Taylor, and B. B. Jarvis(2003). Stachybotrys chlorohalonata, a new species from water-damaged buildings, Mycologia 95, 1228-1237.
D. M. Kuhn and M. A. Ghannoum (2003). Indoor Mold, Toxigenic Fungi, and Stachybotrys chartarum: Infectious Disease Perspective. Clinical Microbiology Reviews, 16 (1), 144–172
S. Li, G. L. Hartman, B. B. Jarvis, and H. Tak, A (2001). Stachybotrys chartarum Isolate from Soybean." Mycopathologia, 154, 41-49.
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ABOUT THE AUTHOR:
Dr. Jackson Kung’u is a Microbiologist who has specialised in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analysed thousands of mould samples from across Canada. Jackson provides how-to advice on indoor mould and bacteria issues. Get more information about indoor mould and bacteria at http://www.moldbacteria.com.
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